This invention relates generally to carriers for holding articles during processing and more particularly to a carrier for holding wafers during chemical vapor deposition on the wafers.
It is common practice in the processing of semiconductor material (typically in the form of a wafer) to deposit a layer or film of polycrystalline semiconductor material on one face of the wafer. In the integrated circuit formed from the semiconductor wafer, the layer may provide conducting regions, electrical insulation between metals and/or protection from the environment. For example, a layer of polycrystalline silicon on a monocrystalline silicon may be used for gettering, or as the gate electrode material in MOS integrated circuit devices.
Although many methods are available for depositing a layer of material on the monocrystalline semiconductor wafer, chemical vapor deposition processes are most frequently employed. Generally, the wafer is held on a carrier in a heated reactor through which gas containing the material to be deposited in a vaporous form is circulated. The decomposition of the gas on the semiconductor wafer produces the layer. The most common process is referred to as low pressure chemical vapor deposition, or LPCVD.
As with all processing of semiconductor wafers, it is important that the wafer not be damaged during LPCVD. However, it has been found that wafers are occasionally chipped when removed from the carrier after the LPCVD because of the breakage of bridges of polycrystalline material which join the wafers to the carrier. The bridges are formed by polycrystalline material deposited from the gas onto the wafer and the carrier. A presently existing carrier used in LPCVD of polycrystalline silicon layers on silicon wafers supports and holds the wafers using four quartz rods held together by a frame. Small sections of the peripheral edges of the wafers are received in respective slots in of the rods, such that the wafers are held in an upright position. The wafers engage the rods only over small areas, amounting essentially to a point contact between the wafer and the rod. It is believed that the geometry of the rods and the slots permits the polycrystalline silicon vapor to access the points where the wafer engages the rods in the slots and build up substantial material bridges. The more material deposited in bridges connecting the wafer to the carrier, the more likely chipping of the wafer will occur when removed from the carrier.